View the instructions here: http://blog.inventables.com/2014/04/upgrading-your-shapeoko-2-with-nema-23.html
The ShapeOko 2 is compatible with NEMA 23 motors, with a few modifications to the basic assembly. The machine runs fine with NEMA 17 motors, but if you decide to modify the basic design to longer extrusions or a larger more powerful spindle you may want to use NEMA 23 motors for the X and Y axes. They will give you the power and speeds appropriate for a larger machine.
The larger motors need to be mounted on the 1/4" spacers to clear the bolt heads for the idler pulleys. You also have to avoid the bolts used to mount the X axis MakerSlide. This is done by moving the motor to the lower end of the slots or by notching the MakerSlide.
To get the most out of the motor upgrade, you can use the tinyG controller with the Enclosed Power supply. However, the upgrade would work with the stock power supply and gShield.